The invention relates to apparatus and a method for coating a web traveling through a coating machine wherein passage of a web seam underneath a coating knife blade is facilitated by a floating backward arcuate movement of the knife blade, with increasing pressure against the seam portion to maintain contact. The apparatus may also be advantageously utilized to maintain a constant blade pressure against the fabric in a floating mode.
Fabric is coated in web form traveling through a coating machine where lengths of fabric are joined together by a thickened seam portion whereby a continuous web can be provided traveling through the coating machine. In certain type of coating machines a knife blade is carried over a roller or other supporting surface and the web travels between the blade and support roller. Coating compound is applied to the fabric prior to passing underneath the coating blade. The coating blade then spreads the coating compound into and over the fabric. However, passage of the thickened seam portion underneath the coating blade without damage to the seam or without the application of an irregular or excessive amount of coating is a problem to which considerable attention need be given.
In blade-over-roller coating machines employing a trough feed system, the problem becomes even more severe due to the utilization of a metering gap between an open edge of the trough and the coating blade for feeding the coating compound onto the fabric. This increases the problems of excessive and irregular coating of the fabric at the seam portion. This also renders it more difficult to support the coating knife blade in a movable fashion to avoid damage to the fabric by engagement with the knife blade edge. The knife blade is set closely on the surface of the fabric for spreading the coating compound over and into the fabric. Often the coating knife blade must be held against the fabric with a certain amount of pressure for satisfactory coating. Thus, due to the closeness of the blade against the fabric and the pressure, considerable seam damage can occur.
Heretofore, it has been proposed to provide a pivotal coating blade on a coating machine. The blade is held down by an air cylinder which exerts a slight air pressure on the blade which allows it to pivot upward when hit by the seam. The air pressure is a constant preset value, and does not satisfactorily enable the blade to ride over the seam in contact therewith. Furthermore, the slight air pressure which is needed on the air cylinder to allow it to pivot often does not return the blade after seam passage. Efforts to increase the air pressure to return the blade to its blade down position have made it difficult for the blade to lift when engaged by a seam. Furthermore, the above described system is only usable for very thin blades, such as two or three inches in height which are easily deflectable.
U.S. Pat. Nos. 3,176,651 and 2,534,320 disclose puddle coating machines. In this type of machine a traveling web passes over the surface of a rotating backup roll, and a trailing doctor blade is applied to the web surface. A puddle of coating material is provided between the blade and the traveling web. However, this is a different coating process and apparatus than one which utilizes a vertically disposed coating blade arranged over a coating roller, and a trough feed system for supporting a coating compound above a traveling fabric web. While mechanisms are employed in the aforesaid patents for applying a uniform pressure on the blade against the web, this would not facilitate passage of a thickened seam portion of the web in a suitable manner.
Accordingly, an important object of the present invention is to provide an apparatus and method which compensates for the passage of a thickened seam portion on a web traveling through a coating machine.
Still another important object of the present invention is to provide an apparatus and method for accommodating the passage of a thickened seam portion underneath a coating blade on a blade-over-roller coating machine employing a trough feed system.
Still another important object of the present invention is to provide a method and apparatus for compensating for seam passage on a coating machine wherein a coating blade is positively guided in a floating backward arcuate motion to facilitate passage of a thickened seam portion.
Still another important object of the present invention is to provide a method and apparatus for a coating machine which accommodates the passage of a thickened seam portion underneath a coating blade wherein the coating blade is counterbalanced against the web with an increasing force so that the blade does not bounce out of contact when impacted initially by the seam, but is caused to ride over and maintain contact with the seam.
Still another important object of the present invention is to provide an apparatus and method for mounting a blade assembly unit on a coating machine which includes a trough feed system and a coating blade which are set a predetermined distance apart to create a metering gap wherein the entire assembly moves in a backward arcuate motion upon impact with a seam portion of a web traveling beneath the trough and blade.
Still another important object of the present invention is to provide a movable blade assembly unit on a coating machine which guides a coating blade in a floating backward arcuate motion upon engagement with a seam having a greater horizontal component than vertical component to reduce the initial inertial impact forces.
Still another important object of the present invention is to provide an apparatus and method for biasing and guiding a movable coating blade against a web so that a thickened seam of the web moves the coating blade a greater distance horizontally than vertically on initial impact, and then lifts the blade over the seam whereby seam damage is prevented and even coating of the seam is achieved.